Investments (Securities Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	$ 2,728,343	$ 2,577,275
Gross Unrealized Gains, Debt securities	118,021	143,234
Gross Unrealized Losses, Debt securities	(22,811)	(9,132)
Fair Value, Debt securities	2,823,553	2,711,377
Amortized Cost, Equity securities		12,799
Gross Unrealized Gains, Equity securities		4,849
Gross Unrealized Losses, Equity securities		(345)
Fair Value, Equity securities		17,303
Amortized Cost	2,740,993	2,590,074
Gross Unrealized Gains	122,658	148,083
Gross Unrealized Losses	(23,062)	(9,477)
Fair Value	2,840,589	2,728,680
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	760,948	100,678
Less than 12 Months, Unrealized Losses	(17,305)	(3,042)
12 Months or Greater, Fair Value	121,207	211,706
12 Months or Greater, Unrealized Losses	(5,757)	(6,435)
Total, Fair Value	882,155	312,384
Total, Unrealized Losses	(23,062)	(9,477)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,823,553	2,711,377
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	757,959	100,373
Less than 12 Months, Unrealized Losses	(17,109)	(2,990)
12 Months or Greater, Fair Value	119,829	207,905
12 Months or Greater, Unrealized Losses	(5,702)	(6,142)
Total, Fair Value	877,788	308,278
Total, Unrealized Losses	(22,811)	(9,132)
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	588	589
Gross Unrealized Gains, Debt securities	0	0
Gross Unrealized Losses, Debt securities	(53)	(36)
Fair Value, Debt securities	535	553
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	535	553
12 Months or Greater, Unrealized Losses	(53)	(36)
Total, Fair Value	535	553
Total, Unrealized Losses	(53)	(36)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	9,943	9,939
Gross Unrealized Gains, Debt securities	482	386
Gross Unrealized Losses, Debt securities	0	0
Fair Value, Debt securities	10,425	10,325
Public Utilities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	150,042	169,179
Gross Unrealized Gains, Debt securities	8,407	10,163
Gross Unrealized Losses, Debt securities	(480)	(126)
Fair Value, Debt securities	157,969	179,216
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	17,472	0
Less than 12 Months, Unrealized Losses	(480)	0
12 Months or Greater, Fair Value	0	14,827
12 Months or Greater, Unrealized Losses	0	(126)
Total, Fair Value	17,472	14,827
Total, Unrealized Losses	(480)	(126)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,512,794	2,334,700
Gross Unrealized Gains, Debt securities	105,156	128,280
Gross Unrealized Losses, Debt securities	(22,270)	(8,961)
Fair Value, Debt securities	2,595,680	2,454,019
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	740,487	100,373
Less than 12 Months, Unrealized Losses	(16,629)	(2,990)
12 Months or Greater, Fair Value	114,467	187,699
12 Months or Greater, Unrealized Losses	(5,641)	(5,971)
Total, Fair Value	854,954	288,072
Total, Unrealized Losses	(22,270)	(8,961)
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	42,184	48,674
Gross Unrealized Gains, Debt securities	3,734	4,116
Gross Unrealized Losses, Debt securities	0	0
Fair Value, Debt securities	45,918	52,790
Home Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	11,381	11,702
Gross Unrealized Gains, Debt securities	199	225
Gross Unrealized Losses, Debt securities	(8)	(9)
Fair Value, Debt securities	11,572	11,918
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	4,827	4,826
12 Months or Greater, Unrealized Losses	(8)	(9)
Total, Fair Value	4,827	4,826
Total, Unrealized Losses	(8)	(9)
Manufactured Housing [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	1,411	2,492
Gross Unrealized Gains, Debt securities	43	64
Gross Unrealized Losses, Debt securities	0	0
Fair Value, Debt securities	1,454	2,556
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	17,036	17,303
Equity Public [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities	12,650
Gross Unrealized Gains, Equity securities	4,637
Gross Unrealized Losses, Equity securities	(251)
Fair Value, Equity securities	17,036
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	2,989	305
Less than 12 Months, Unrealized Losses	(196)	(52)
12 Months or Greater, Fair Value	1,378	3,801
12 Months or Greater, Unrealized Losses	(55)	(293)
Total, Fair Value	4,367	4,106
Total, Unrealized Losses	$ (251)	$ (345)